1. Field of Invention
This invention relates to precision wavelength illumination selection for a machine vision system.
2. Description of Related Art
Conventional machine visions systems perform dimensional measurements of specific target features of a sample workpiece. Such an application is applied, for example, in measuring the position or other characteristic of specific target features of a sample workpiece for comparison to a standard or reference value of the position or other characteristic of the workpiece. In such an application, for different surface colors or color patterns that overlap, appropriate selection of color illumination can enhance the image contrast between different portions of such multi-colored targets. One system for measuring a pattern or feature places a target to be observed on a stage. Thereafter, full spectrum illumination is used by shining a beam of light from a halogen lamp, for example, onto the target and then measuring the target features. However, discriminating between overlapping features can be difficult because the contrast between the features is poor when using full spectrum illumination.
Another system for measuring a feature uses a plurality of discrete light sources, each of which emits a beam of light having a different color. To obtain a desired illumination setting, the current or voltage to each of the plurality of light sources is varied until the combination of the beams of light create the desired illumination setting.
It is also known to illuminate workpieces with light passing through one or more filters of a set of candidate filters to create a desired wavelength illumination that will be applied to a specific target feature. One such system is disclosed in, for example, U.S. Pat. No. 6,152,577 to Rizkin et al., which discloses a remote illumination system. The system of the 577 Patent uses a movable device with different color filters placed in each of a number of equally spaced openings. When selecting a particular color of illumination, the device is moved until the desired filter is selected. However, this system is problematic in that the amount of illumination settings available is limited to the number of openings in which a filter can be placed. Thus, desired illumination is not easily obtained if the opening does not have that specific color filter.